EP0021205B1 - Hybrid compression-absorption method for operating heat pumps or refrigeration machines - Google Patents

Description

The invention relates to a hybrid compression absorption method for operating heat pumps or refrigerators, with a working medium consisting of a solvent and a refrigerant soluble therein, in which in a first heat exchange process the refrigerant is dissolved in the solvent with heat removal and after expansion as a liquid phase the solvent and the refrigerant dissolved therein from the first heat exchange process, the working medium which is supplied with heat in a second heat exchange process, and thereby the refrigerant dissolved in the solvent at least partially as. Vapor phase is expelled, and the vapor phase of the working medium drawn off from the second heat exchange process is compressed in a compression process, the concentration of the refrigerant in the liquid phase of the working medium being continuously changed along the path of the working medium by the second heat exchange process, preferably also by the first heat exchange process.

The invention further relates to a hybrid refrigerator or heat pump for carrying out the method.

The possible uses of heat pumps and the increase in their effectiveness are being explored with increased intensity everywhere in the world due to the energy crisis. The heat pump is actually a reversed chiller that transfers the energy from the environment into a functionally closed space.

The currently known compression heat pumps are mostly operated with refrigerants commonly used in refrigeration technology. The trend of the research also points towards the refinement of the methods already proven in refrigeration technology and the application of the methods for the heat pumps. However, one cannot expect a significant breakthrough from this development trend.

There are also cooling tasks where a medium with a variable temperature (a cooling medium) is to be cooled and the extracted energy is also to be transferred to a medium with a variable temperature (e.g. cooling water). In such cases, the conventional compression refrigeration machines have the major disadvantage that the evaporation and condensation temperatures of the refrigeration machine on the side of the heat exhaust are below the lowest temperature of the medium to be cooled, and on the side of the heat output the highest temperature of the heat-absorbing medium must, and that - which is closely related - the pressures of the heat exchanger vessels must be determined with an unnecessarily large deviation. So the value of the pressure ratio, which basically determines the operation of the compressor, becomes rather unfavorable. The same problem also occurs with heat pumps.

Compression processes are also known (DE-B-1 241 468), in which a mixture of two refrigerants with different boiling points is used, the higher-boiling component being liquefied by partial condensation from the compressed refrigerant-vapor mixture, separated from the lower-boiling vaporous component and is relaxed and evaporated to liquefy the lower-boiling component, whereas the liquefied lower-boiling component is expanded and evaporated and mixed with the relaxed higher-boiling component again before evaporation, after which the vaporous higher-boiling component and the vaporous lower-boiling component mixed with it are compressed again together.

In addition, however, it is already known to combine the absorption process and the compression process with one another. In such a known method (DE-A-2538730), a refrigerant, such as a halogenated hydrocarbon, which can be condensed in the operating range of the method and a solvent compatible with it, such as an oil, is used as the working medium, and the method is carried out in this way that only part of the refrigerant, for example half or less, is dissolved in the solvent during the absorption process. After leaving the absorber, which is designed as a flooded standing tube bundle heat exchanger with an overhead common inlet for the vapor phase of the refrigerant and the liquid solvent, the remaining refrigerant portion is separated from the refrigerant-enriched solution and in a degasser, which is the standing one Tube boiler with inlet below for the solution enriched with refrigerant in the absorber after its relaxation, brought into the heat exchange with the rich solution and partially condensed so that the refrigerant is expelled from the solution by the evaporation heat released. The expelled refrigerant and the liquid solvent are sucked out of the overhead drain of the degasser into a compressor, in which also that part of the refrigerant that was used in the degasser to expel the refrigerant portion absorbed in the solvent is full constant condensation and subsequent evaporation is sucked in. In this known method, therefore, the compressor compressing the refrigerant vapor is additionally used to suck the working medium through the degasser and to pump the liquid solvent to the high-pressure side of the absorber, so that an additional solvent pump can be dispensed with. Since an oil is also used as a solvent, it is also used for lubrication by passing it through the compressor, which is, for example, a screw compressor. However, since developments in this process with an excess of refrigerant is the Verdichtun ^g sarbeit high.

In another known hybrid compression absorption method (DE-A-2617351) of the type mentioned at the beginning, the working medium used is e.g. Amoniak and water used. The refrigerant expelled from the liquid solvent in the second heat exchange process is separated from the solvent, the vapor phase consisting of the separated refrigerant is returned to the first heat exchange process after compression, while the liquid phase consisting of the separated, low-refrigerant solution is pumped an inner heat exchanger, in which the liquid phase in countercurrent to the solution, which is drawn from the second heat exchange process and is rich in absorbed refrigerant, is heated before being released from the latter, is returned to the first heat exchange process and is brought back together with the compressed refrigerant vapor there. This known method shows that. the efficiency can be significantly increased if both in the first heat exchange process for the absorption of the compressed refrigerant in the solvent, and in the second heat exchange process for expelling the refrigerant from the solvent, the solvent in countercurrent to the heat to be supplied in the heat exchange processes or laxative external heat transfer medium is performed. By using the countercurrent principle it can be achieved that the temperature of the heat transfer medium changes continuously over the heat exchange surface and that the temperature of the solution on the other side of the heat exchange surface follows, so that in the solution of the solvent and the absorbed refrigerant in both Degassing process as well as in the absorption process, a state of equilibrium of the solution concentration and temperature which is continuously changed from the beginning to the end thereof. This goal is impaired in the known method, however, in that a vapor space for the refrigerant is formed over the entire liquid space of the absorber and the degasser, so that the liquid phase with its different temperature and concentration states along the absorber or degasser equilibrium of the entire gas phase, which has practically the same state parameters over the entire liquid phase.

In another known combined compression-absorption method (DE-C-84084), after the separation of the vapor phase from the liquid phase of the working medium drawn off from the degasser. the vapor phase is compressed and recombined with the liquid phase after it has been heated in an internal countercurrent heat exchanger by the refrigerant-rich solution drawn off from the absorber while cooling, before entering the absorber. In the degasser, which can also be understood as an evaporator, the working medium is led through a coil and thereby extracts heat from a room to be cooled. Pipe coil evaporators of this type, in which a course for the working medium is brought about by the course of the pipe coil, are also referred to as dry evaporators in contrast to flood evaporators, in which the wetting of the heat exchange surface with the liquid phase is increased. However, since in this known method the temperature on the heat-emitting side of the degasser to be cooled is practically constant over the entire length of the coil, there is no significant continuous increase in temperature between the entry and exit of the degasser and therefore a decrease in the concentration of the refrigerant in the solvent corresponding to that described above other known method (DE-A-2617351) where this goal is achieved by utilizing the countercurrent principle.

In addition, in the known methods, the superheating of the refrigerant vapor in the compressor is high, which limits the possible pressure ratio.

The invention solves the problem of designing a hybrid compression absorption method of the type mentioned at the beginning and a hybrid refrigeration machine or heat pump for carrying out the method in such a way that a higher energy efficiency can be achieved while avoiding the disadvantages of the known methods mentioned.

This is achieved according to the invention in that the solvent is partially evaporated by the heat supply in the second heat exchange process, that along the path of the working medium through the second heat exchange process, preferably also through the first heat exchange process, the concentration of the refrigerant also in the steam phase of the working medium is changed simultaneously and together with that of the liquid phase, and that the compression process is subjected to the vapor phase and the liquid phase of the working medium, which are drawn off from the second heat exchange process, simultaneously and together.

To carry out the method according to the invention, a hybrid refrigeration machine or heat pump with a working medium circuit is preferred, which contains an absorber, a degasser connected downstream thereof via an expansion valve and a mechanical compressor connected downstream thereof, the absorber and the degasser being designed as such heat exchangers that Due to their construction between their inlet and outlet a common path for the working medium, which is formed by guiding elements, is brought about between the liquid phase and the vapor phase of the working medium, that an internal countercurrent heat exchanger is connected between the absorber and the expansion valve on the one hand and between the degasser and the compressor on the other hand is, and that the output of the degasser is connected to the compressor without branching via the internal heat exchanger.

In the sense of the invention, in a working medium consisting of a refrigerant and a solvent circulating system, provided with a mechanical compressor, at least one of the heat exchangers that enables heat exchange with the environment is a so-called "dry" one that suitably consists of pipes or plates. Construction by means of which continuously changing concentration ratios and / or clearly assigned, continuously changing temperature ratios between the initial and final states are guaranteed both with respect to the liquid phase and the vapor phase of the working medium. In addition, since the vapor phase, which also contains a portion of solvent vapor, and the liquid phase of the working medium are present simultaneously and together in the compressor work space, the mixing of the vapor and liquid phases and the dissolving of the steam run in parallel with the pressure increase during compression, so that the regularities of the thermodynamics of the solutions are also used in the compression process.

• Fig. 1 die Grundschaltung der erfindungsgemäßen hybriden Wärmepumpe und
• Fig. 2 eine weitere zweckmäßige Ausführungsform der erfindungsgemäßen Wärmepumpe.

The invention is explained in more detail with reference to the drawing, in which possible circuit diagrams of the hybrid refrigerator or heat pump according to the invention are shown. Show it:

• Fig. 1 shows the basic circuit of the hybrid heat pump according to the invention and
• Fig. 2 shows another useful embodiment of the heat pump according to the invention.

1 shows the basic type of the hybrid heat pump according to the invention. As can be seen from the figure, the system, in the thermodynamic system of which a working medium consisting of a solvent and a refrigerant soluble therein is circulated, has an absorber 1 and a degasser 4 as a heat exchanger. An internal heat exchanger 2 (temperature changer) and a pressure-reducing expansion valve 3 (expediently a throttle valve) are arranged between the absorber 1 and the degasser 4. Behind the degasser 4 there is an inner heat exchanger 2, in which the working medium emerging from the degasser 4 flows in countercurrent to the solution emerging from the absorber 1 and from which the path of the working medium leads to a mechanical compressor 8, the outlet of which with the absorber 1 is connected.

The operation of the system is as follows: The solution emerging from the absorber 1 flows through one side of the inner heat exchanger 2 and through the expansion valve 3. After flowing through the pressure-reducing expansion valve 3, a solution of low pressure passes into the degasser 4 removes heat from the medium to be cooled. Due to the amount of heat qq extracted from the medium to be cooled, refrigerant and solvent are transferred to the vapor phase of the working medium, which means that this amount of heat drives the refrigerant out of the solution and evaporates the solvent portion and provides the necessary heat of solution and evaporation.

In the degasser 4 there is thus a two-phase flow, the constructive design of the degasser 4 as a so-called "dry" construction, which is characterized by the formation of a forced path for the working medium between the inlet and the outlet of the working medium, which is brought about by guide elements such as pipes or plates Heat exchanger, the proportion of the vapor phase along the heat exchanger surface gradually defined-increases. Depending on this, the temperature of the flowing system increases according to the laws of the solutions.

The two-phase mixture emerging from the degasser 4 passes through the other side of the internal heat exchanger 2 into the compressor 8, which q is the two-phase working medium through the use of mechanical work _. compressed to the higher pressure level of the absorber 1.

From the compressor 8, the high-pressure liquid-vapor mixture flows back into the absorber 1, where the heat of vaporization and the heat of solution of the refrigerant, ie the amount of heat q _o , change with a change Temperature sequence is withdrawn or used for heating purposes.

According to the same design principles as in the degasser 4, the heat exchange surface of the absorber can also be uniquely assigned a temperature field that changes along the same; the heat given off can therefore really be used with changing temperature parameters.

The use of the internal heat exchanger 2 improves the thermal efficiency of the system.

In the system according to the invention, therefore, the phases of the two-phase working medium emerging from the degasifier 4 are not separated, but instead pass after passing through the internal heat exchanger 2. together and at the same time in the working space of the compressor 8, where, in addition to the compression, the physical processes determined by the thermodynamics of the solutions also take place.

In addition to the vapor phase, the liquid can even be present in two different forms. On the one hand, according to one solution, the liquid phase can occur in its specifically liquid form. On the other hand, however, it can also be present in the form of aerosol in the steam. A suitable pump and also an atomizer are of course also required for the latter embodiment.

A very great advantage of this "wet" compression lies in the fact that during the compression the mixing of the vapor phase and the liquid phase of the working medium and the dissolving of the vapor in parallel with the. Pressure increase takes place, whereby the vapor phase and the liquid phase strive to achieve a balance in function of time and reaction rates - according to the laws of the thermodynamics of the solutions. However, the temperature values belonging to these equilibrium states are always significantly lower than the temperature values belonging to a given pressure in the case of adiabatic compression.

With regard to the vapor phase, this situation can be assessed as if a uniform and continuous recooling process was taking place in parallel with the compression. The energetic meaning of this phenomenon is well known to a person skilled in the art. Another effect which reduces the compression work arises from the fact that the mass fraction of the vapor phase also decreases during the dissolving process, and less vapor has to be compressed in this way.

In addition to the phenomena described, the final temperature of the compression also decreases, which is of crucial importance with regard to the design features of the compressor and the materials that can be used. The pressure ratio of the single-stage compression can be increased significantly, whereby the goal can be achieved with simpler and cheaper means.

Due to the properties mentioned, this embodiment can achieve significant advantages.

The embodiment according to FIG. 2 has the advantage that it combines the good properties of the working medium circuit discussed in FIG. 1 and the absorption machines as the drive circuit, since this embodiment from FIG. 2 functions without external mechanical energy expenditure by introducing thermal energy.

The most important advantage of this embodiment compared to the absorption chiller serving as the starting point is that it can be used to bridge a very large temperature difference between the heat exchangers, or, given the same external environmental conditions, this system according to the invention has almost twice the performance figure ε:

The liquid working medium flows from the absorber 1 in the already known manner over one side of the inner heat exchanger 2 and the pressure-reducing expansion valve 3 into the degasser 4, in which the working medium from the environment thermal energy q _. withdrawn, as a result, part of the working medium evaporates.

The remaining liquid phase and the vapor phase pass through the other side of the inner heat exchanger 2 into the compressor 8, in which the "wet" compression takes place.

The working medium is pressed by the compressor 8 into the absorber 19 of the drive circuit. Here the vapor phase of the working medium is condensed and the refrigerant is dissolved in a poor solution coming from a boiler 18, the working medium giving off its heat of evaporation and solution q _o2 .

From the absorber 19, the rich solution flows with the aid of a solution pump 6 via one side of an inner heat exchanger 12 of the drive circuit into the boiler 18, in which the rich refrigerant vapor is expelled from this rich solution with the help of an external amount of energy q _k high temperature levels becomes.

The poor solution flows back over the other side of the inner heat exchanger 12 and the pressure-reducing expansion valve 3 into the drive-side absorber 19.

The steam leaving the boiler 18 flows into a mechanical expansion machine 17, in which a part of the enthalpy of the steam in mechanical energy is converted. The compressor 8 is driven by this mechanical energy.

The steam leaving the expansion machine 17 reaches the absorber 1 and the thermodynamic circuit is thus closed.

In this embodiment, it can also be mentioned that the working medium emerging from the compressor 8 could also be conducted into the absorber 1, the steam emerging from the expansion machine 17 having to be conducted into the drive-side absorber 19. This could thermodynamically separate the working side and the drive side. This way of switching is less interesting because it means no further advantages in terms of function; it even results in a certain deterioration of the specific parameters because in the. in the former case, higher temperatures can be achieved by appropriately selecting the concentration ratios on the drive side in the absorber 19, as a result of which a larger proportion of the energy expended can be obtained at a higher temperature level.

In summary, it can thus be stated that the heat pump according to the invention has a very wide field of application, because from the deep-freezing tasks to the heating purposes, it guarantees more energy-efficient operation than the previous systems.

Another advantage of the system according to the invention is that it can be adapted very flexibly to the task to be solved, depending on the concentration ratios of the solution used, and in this way its operating characteristics can be optimized.

Claims (5)

1. Hybrid compression-absorption method for operating heat pumps or refrigeration machines, with a working medium consisting of a solvent and a refrigerant soluble therein, in which in a first heat-exchange action, the refrigerant is dissolved in the solvent, heat being withdrawn, and after expansion of the working medium removed from the first heat-exchange action as liquid phase consisting of the solvent and the refrigerant dissolved therein, heat is supplied to this medium in a second heat-exchange action and thus the refrigerant dissolved in the solvent is at least partially expelled as vapour phase, and in a c0mpressi0n` action the vapour phase of the working medium withdrawn from the second heat-exchange action is compressed, the concentration of the refrigerant in the liquid phase of the working medium being continuously varied along the path of the working medium through the second heat exchange action, characterised in that by the supply of heat in the second heat-exchange action the solvent is also partially evaporated, in that along the path of the working medium through the second heat-exchange action, preferably also through the first heat-exchange action, the concentration of the refrigerant in the vapour phase of the working medium too is varied continuously, simultaneously and in common with that of the liquid phase, and in that the vapour phase and the liquid phase of the working medium, which are withdrawn from the second heat-exchange action, are subjected simultaneously and in common to the compression action.

2. Method according to claim 1, characterised in that the working medium withdrawn form the first heat-exchange action is brought before the compression action in countercurrent into interior heat-exchange with the working medium before the expansion.

3. Method according to claim 1 or 2, characterised in that the working medium withdrawn from the compression action is mixed in a third heat-exchange action, heat being withdrawn, with a solution poor in refrigerant and thus its vapour phase is condensed and the refrigerant thereof is absorbed, in that then in a fourth heat-exchange action by supply of heat the refrigerant is expelled and a part of the solvent is evaporated out of the refrigerant-rich solution withdrawn from the third heat-exchange action, in that the consequent refrigerant-poor solution is brought into heat exchange with the refrigerant-rich solution withdrawn from the third heat-exchange action and thereafter expanded and returned into the third heat-exchange action, and in that the refrigerant and solvent vapour withdrawn from the fourth heat-exchange action is expanded, mechanical energy being generated which is used as drive energy of the compression action, and returned into the first heat-exchange action.

4. Hybrid refrigeration machine or heat pump for carrying out the method according to Claims 1 and 2, having a working medium cycle which contains an absorber (1), a gas extractor (4) connected by way of an expansion valve (3) after the absorber, and a mechanical compressor (8) placed after the gas extractor, characterised in that the absorber (1) and the gas extractor (4) are formed as heat exchangers of such kind that, due to their design, between their entry and exit a constrained path for the working medium formed by guide elements and common to the liquid phase and the vapour phase of the working medium is brought about, in that between the absorber (1) and the expansion valve (3) on the one hand and between the gas extractor (4) and the compressor (8) on the other an inner countercurrent heat exchanger (2) is placed, and in that the exit of the gas extractor (4) is connected by way of the inner heat exchanger (2) to the compressor (8) without conduit branching.

5. Hybrid refrigeration machine or heat pump according to claim 4, for carrying out the method according to claim 3, characterised in that the exit of the compressor (8) is connected to an absorber (19) of a drive cycle which comprises a boiler (18) following its absorber (19), which boiler is connected on the liquid phase side through a second expansion valve (3) to the absorber (19) of the drive cycle and on the vapour side through a mechanical expansion machine (17), which is coupled with the compressor (8) as its drive, to the absorber (1) of the working medium cycle, while an inner heat exchanger (2) is interposed between the boiler (18) and the expansion valve (3) of the drive cycle on the one hand, and its absorber (19) and the boiler (18) on the other hand.

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